The present invention relates to a reflector type prism having the function of reflecting an incoming beam in a direction that is the reverse of the incoming direction, and a reflector type prism forming die.
In the prior art, a light sensor 109 constituted of a light-emitting element 105 and a light-receiving element 107 and a reflector type prism 111 are employed to detect the number, the traveling speed and the like of bodies to be detected 103, such as sheets of paper that are traveling on a conveyor 101, as illustrated in FIG. 8. The light sensor 109 and the reflector type prism 111 are positioned at opposing sides of the conveyor 101, and face each other.
As illustrated in FIG. 9, the reflector type prism 111 has the function of reflecting a light beam A emitted by the light-emitting element 105 in a direction that is the reverse of its incoming direction to cause the light to strike the light-receiving element 107 as a light beam B. Consequently, the bodies to be detected 103 block the light beam A and the light beam B as they travel on the conveyor 101. The blocking of the light beams A and B by a body to be detected 103 is detected by the light-receiving element 107, so that the light sensor 109 can make decisions as to the presence/absence of a body to be detected 103, its state and the like, based upon this information.
Since a high degree of accuracy is required in setting the optical axes of the light beams A and B, it is crucial that the positioning process for mounting the light sensor 109 and the reflector type prism 111 at specific mounting members be implemented with a high degree of precision. Thus, both a light-emitting surface 109a and a light-entering surface 109b of the light sensor 109 are formed as projecting portions so that the light sensor 109 can be mounted with ease and accuracy to one of the guides of the conveyor 101, i.e., a guide 101a. Likewise, both alight-entering surface 111a and a light-emitting surface 111b of the reflector type prism 111 are formed as projecting portions so that the reflector type prism 111 can be mounted with ease and accuracy to another guide 101b of the conveyor 101. It is to be noted that the reflector type prism 111 formed in the shape described above and having the function described above is constituted of a raw material such as an acrylic resin, a polycarbonate resin or the like and, as illustrated in FIG. 10, it is formed using a die 113.
However, since the reflector type prism 111 shrinks to a certain degree during its formation using the die 113, there is a concern that the light-entering surface 111a and the light-emitting surface 111b may be formed as concave surfaces relative to the direction of the light beams A and B, as illustrated in FIG. 11. If the light-entering surface 111a and the light-emitting surface 111b form concave surfaces in this manner, the light beams A and B become scattered, and ultimately, the quantity of light in the light beam B reaching the light-receiving element 107 of the light sensor 109 becomes reduced. In particular, if the quantity of light in the light beam B is less than a specific value when the distance between the light sensor 109 and the reflector type prism 111 is great or when a high S/N ratio is required, the light-receiving element 107 may erroneously detect a body to be detected 103, causing erroneous operation in various types of processing performed based upon a detection signal (not shown)output by the light sensor 109.
In addition, the reflector type prism 111 is mounted at the conveyor 101 by inserting the projecting portion upon which the light-entering surface 111a is formed and the projecting portion upon which the light-emitting surface 111b is formed into through holes h1 and h2, respectively, that are provided in the guide 101b for positioning, and then by securing the reflector type prism 111 with a separate mounting blade spring or the like (not shown). Thus, the structure through which the reflector type prism 111 is mounted to the guide 101a in the prior art is complicated, causing an increase in production cost and an increase in the number of work steps.
Furthermore, since the reflector type prism 111 in the prior art is colorless and transparent, a so-called random external light C unrelated to the light beam A may enter the reflector type prism 111 through a portion other than the light-entering surface 111a, as illustrated in FIG. 8, to reach the light-receiving element 107. This presents a problem in that it may cause the light-receiving element 107 to operate erroneously, making accurate detection of the body to be detected by the light sensor 109 impossible.